1. Field of The Invention
The present invention relates to an improved process for efficiently producing a high quality ink jet head for discharging ink as a printing droplet by way of an ink jet system, to perform printing for a printing medium.
2. Related Background Art
There are known a number of ink jet heads used in an ink jet system for performing printing. These ink jet heads are usually provided with a discharging outlet of discharging ink (that is, an ink discharging outlet), a liquid chamber containing ink to be supplied to the discharging outlet, a liquid pathway which communicates the discharging outlet with the liquid chamber, an energy generating element which is disposed at a given portion of the liquid pathway and which generates energy utilized for discharging ink from the discharging outlet, and an ink supply port for externally supplying ink into the liquid chamber.
As for the production of such ink jet head, there is known a process wherein a first substrate for an ink jet head which is provided with energy generating elements and a second substrate made of a glass or metal which is provided with a recess for forming discharging outlets, liquid pathways and a liquid chamber and which is also provided with a port (which serves to supply ink therethrough) to be communicated with a liquid chamber to be formed are provided, the second substrate is laminated to the first substrate with the use of an adhesive while positioning them to establish a liquid chamber and a plurality of liquid pathways each having a discharge outlet wherein each of the liquid pathways contains one of the energy generating elements positioned therein, whereby obtaining a ink jet head. Other than this, there is also known a process wherein a first substrate for an ink jet head which is provided with energy generating elements and a second substrate made of a glass or metal which is provided with a port (which serves to supply ink therethrough) to be communicated with a liquid chamber to be formed are provided, a dry film made of a photosensitive resin is laminated on the energy generating elements-bearing surface of the first substrate, the dry film laminated on the surface of the first substrate is subjected patterning to form a recess for forming a plurality of liquid pathways each containing one of the energy generating element and a liquid chamber, and the second substrate is laminated on the treated surface of the first substrate with the use of an adhesive to establish a liquid chamber and a plurality of liquid pathways each having a discharge outlet wherein each of the liquid pathways contains one of the energy generating elements positioned therein, whereby obtaining a ink jet head.
However,. any of these processes have such problems as will be described in the following. That is, in any of these processes, as above described, the second substrate is laminated to the first substrate with the use of an adhesive, in this lamination step, the adhesive has a tendency of flowing into the liquid pathway-forming recesses to make the resulting liquid pathways to be uneven in terms of their shapes. This situation is liable to make an ink jet head obtained such that provides a variation for a state of ink discharged from each discharging outlet, in the worst case.
In order to eliminate the problems in the above described processes, U.S. Pat. No. 4,775,445 (hereinafter referred to as document 1) describes a process for producing an ink jet recording head wherein its liquid pathways are formed without using an adhesive. The process described in document 1 is of the following contents. That is, a substrate for an ink jet recording head which is made of silicon or glass and provided with energy generating elements is provided, and on the energy generating elements-bearing surface of the substrate, there is formed a solid layer having a portion serving to form discharging outlets, liquid pathways and a liquid chamber by laminating a positive or negative type photosensitive dry film on the energy generating elements-bearing surface of the substrate, followed by subjecting the photosensitive dry film on the substrate to patterning by way of photolithography. Thereafter, a liquid hardening material is applied onto the substrate having the solid layer thereon at a desired thickness, followed by hardening the liquid hardening material disposed on the first substrate, to thereby obtain a stacked body. The stacked body thus obtained is immersed in a solvent capable of dissolving the solid layer to remove the solid layer, whereby establishing a plurality of liquid pathways each containing one of the energy generating elements and having a discharging outlet and a liquid chamber. By this, there is obtained an ink jet head (that is, an ink jet recording head).
The process described in document 1 has an advantage in that since the liquid pathways are formed by the substrate and the hardening material wherein the lamination of the substrate with the hardening material is conducted by virtue of an adhesion caused upon hardening the hardening material, there can be obtained a ink jet head without using an adhesive.
However, as for the process described in document 1, there are problems such that the capacity of the liquid chamber is governed by the area of the solid layer resulted by way of the patterning, it is therefore difficult to attain an increased capacity for the liquid chamber so as to be suitable in the case where a great many of liquid pathways are arranged at a high arrangement density, and this situation makes it difficult to obtain an ink jet head having a great many discharging outlets arranged at a high arrangement density which can perform printing at a high speed while smoothly and effectively supplying ink to the liquid pathways.
In view of these problems for the process described in document 1, U.S. Pat. No. 5,030,317 (hereinafter referred to as document 2) describes a process for producing an ink jet head having a liquid chamber with an increased capacity. The process described in document 2 is of the following contents. That is, a first substrate for an ink jet recording head which is made of silicon or glass and provided with energy generating elements is provided, and on the energy generating elements-bearing surface of the first substrate, there is formed a solid layer having a portion serving to form discharging outlets, liquid pathways and a liquid chamber by laminating a positive or negative type photosensitive dry film on the energy generating elements-bearing surface of the first substrate, followed by subjecting the photosensitive dry film on the first substrate to patterning by way of photolithography. Thereafter, a liquid of a material capable of being hardened with the irradiation of active energy rays (this material will be hereinafter referred to as hardening material) is applied onto the substrate having the solid layer thereon to form a liquid layer having a desired thickness. Then on the liquid layer of the liquid hardening material of the first substrate, a second substrate which is made of a material having a property of allowing active energy rays to transmit therethrough and which is provided with an ink supply port is press-contacted to obtain a stacked body. The hardening material layer of the stacked body is subjected to patterning by irradiating active energy rays through the second substrate, wherein the hardening material layer except for a portion of thereof serving to form a liquid chamber is insolubilized to form a latent pattern for the formation of the liquid chamber. The stacked body thus treated is immersed in a solvent capable of dissolving the solid layer and the non-insolubilized hardening material to remove the solid layer and the non-insolubllized hardening material, whereby establishing a plurality of liquid pathways each containing one of the energy generating elements and having a discharging outlet and a liquid chamber. By this, there is obtained an ink jet head (that is, an ink jet recording head).
The process described in document 2 has an advantage in that since the liquid chamber is formed by the foregoing non-insolubilized portion of the hardening material and the solid layer, the liquid chamber can be made to have a relatively large capacity, and because of this, there can be obtained a ink jet head in which ink can be smoothly and effectively supplied ink to the liquid pathways at the time of performing printing at a high speed.
However, the process described in document 2 has drawbacks such that there is a limit for the thickness of the hardening material layer because when the hardening material layer is made to be excessively thickened, the latent pattern for the formation of the liquid chamber cannot be conducted at a desired precision and because of this, it is difficult to attain an increased capacity for the liquid chamber so as to be suitable in the case where a great many of liquid pathways are arranged at a high arrangement density, and this situation makes it difficult to obtain an ink jet head having a great many discharging outlets arranged at a high arrangement density which can perform printing at a high speed while smoothly and effectively supplying ink to the liquid pathways.
Document 2 however describes a manner of making the liquid chamber to have a large capacity by forming a recess capable becoming a part of a liquid chamber at the second substrate and forming the liquid chamber by said recess, the solid layer and the non-insolubilized portion of the hardening material layer.
In any case, there is a problem for the process described in document 2 in that the height of a liquid chamber formed is governed by the thickness of the hardening material layer and also the magnitude of the pressure applied upon the press-contact of the second substrate to the hardening material layer of the first substrate, and because of this, it is difficult to attain a desirable uniformity for the height for a liquid chamber formed in every production lot of an ink jet head. In addition, there is a further problem in that the lamination of the second substrate to the first substrate through the hardening material layer is conducted by way of press-contact as above described, and because of this, the first and second substrates are sometimes laminated in such a state that they are not parallel to each other, wherein the resulting liquid chamber becomes not to have an even height but to have such a height that is positionaly varied, and this situation makes the resulting ink jet head such that the amount of ink supplied into each liquid pathway is varied to provide a variation for the amount discharged from each discharging outlet, resulting in making prints obtained to be varied in terms of quality. In the process described in document 2, in order to attain a uniformity for the height of the liquid chamber, it is necessary to use an independent assembling apparatus (not described in document 2) capable of precisely positioning the first and second substrate upon the lamination of them through the hardening material layer. However, if such assembling apparatus should be used, in the case where the second substrate has an inherent warp, a liquid chamber formed unavoidably becomes to have such a height that is positionaly varied, resulting in entailing such problems as above described.
The above described problems as for the process of document 2 would be not remarkable in the case of producing an ink jet head in which the number of liquid pathways is small but they cannot be disregarded in the case of producing a prolonged ink jet head having a longer discharging outlet than the width of a printing medium which is represented by a so-called full-line type ink jet head.
In order to eliminate such problems found in the process of document 2, U.S. Pat. No. 5,3332,466 (hereinafter referred to as document 3) proposes a process for producing an ink jet head (an ink jet recording head) wherein one or more spacer members are provided at a first substrate (that is, a substrate for an ink jet head) or a second substrate (that is, a top plate) so that the first and second substrates can be laminated in parallel to each other through a hardening material layer. Particularly, the process of document 3 is similar to the process of document 2, except for using the spacer member in the former. It is understood that according to the process of document 3, the first and second substrates can be laminated in parallel to each other through the hardening material layer by the action of the spacer member without using the foregoing assembling apparatus, and because of this, there can be attained the production of an ink jet head having a liquid chamber with a uniform height. Further, it is understood that in the process of document 3, even in the case where the second substrate should be accompanied with a warp, the second substrate is press-contacted to the first substrate while utilizing the action of the spacer member wherein the second substrate is straightened and the thickness of the hardening material layer is not varied.
However, in the process of document 3, each spacer nember is disposed at an end portion of either the first or second substrate where no solid layer is present in order to prevent the solid layer from suffering from a pressure, and because of this, in the case where the central portion of the second substrate is warped toward to the first substrate, it is impossible to straighten the second substrate, wherein a liquid chamber with a varied height is unavoidably formed. In this case, if the warped second substrate is press-contacted through the hardening material layer to the first substrate while straightening the warped second substrate, a stress is remained between the straightened second substrate and the hardening material layer, wherein there is a tendency of causing a removal at the interface between the second substrate and the hardening material layer due to a change in the environmental temperature during the production process.
Further, in any of the processes described in documents 2 and 3, there are problems such that in order to make the hardening material to be uniformly contacted with the second substrate, the hardening material in a relatively large amount is necessary to be applied, wherein a problem is liable to entail in that the hardening material is extruded outside upon the lamination of the first and second substrates through the hardening material, wherein such hardening material extruded scatters to deposit on the exposure apparatus and those hardening materials deposited on the exposure apparatus are eventually hardened to entail a problem of reducing the working efficiency. In addition, in any of the processes of documents 2 and 3, because the hardening material is required to be patterned with the irradiation of active energy rays as above described, only photo-setting resins can be used as the hardening material. Further, the second substrate is required to be constituted by a specific material having a property of allowing active energy rays to transmit therethrough.